The use of plastics and rubbers are widespread. The production of these plastics and rubbers are from the polymerization of monomers which are generally produced from petroleum. The monomers are generated by the breakdown of larger molecules to smaller molecules which can be modified. The monomers are then reacted to generate larger molecules comprising chains of the monomers. An important example of these monomers is light olefins, including ethylene and propylene, which represent a large portion of the worldwide demand in the petrochemical industry. Light olefins, and other monomers, are used in the production of numerous chemical products via polymerization, oligomerization, alkylation and other well-known chemical reactions. Producing large quantities of light olefin material in an economical manner, therefore, is a focus in the petrochemical industry. These monomers are essential building blocks for the modern petrochemical and chemical industries. The main source for these materials in present day refining is the steam cracking of petroleum feeds.
With the increase in demand, other sources for monomers are providing for an increase in supply while becoming economical. Sources include natural gas and coal conversion, wherein the natural gas and coal are converted to oxygenates and subsequently the oxygenates are converted to light olefins. The product stream from an oxygenates to olefins conversion process needs to be purified to recover the light olefins. Due to the different chemistry from the conversion of petroleum feedstocks to light olefins, the separation and clean-up of the process stream from the oxygenates to olefins conversion process is therefore different.
The production of light olefins (e.g., ethylene and propylene) from oxygenates, and in particular methanol, also generates various oxygenate byproducts. While some of these byproducts can be recovered and recycled to the conversion reactor, some of the byproducts are can foul and plug downstream equipment and may also lead to separation issues (e.g., emulsions, foaming, oil entrainment).
In a commercial methanol to olefins (MTO) design, oxygenates are recycled to the MTO reactor, which results in a build-up of concentration of oxygenates in the reactor recycle. As used hereinafter, the common term methanol to olefins, or MTO, is meant to refer to any oxygenate to olefins conversion process that can be covered by this disclosure. While it is desirable to recycle dimethylether (DME) and methanol to maintain high utilization of the MTO feed to hydrocarbon products, recycle of the problematic oxygenates (ketones, aldehydes) leads to processing problems.
Therefore, there remains a need for an effective and efficient process for removing the unwanted or undesirable oxygenates from the recycle stream to an MTO reactor.